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Idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is an idiopathic clinical syndrome used to describe pulmonary fibrosis with (1) histological or imaging pattern of usual interstitial pneumonia (UIP) and (2) absence of alternative causes such as drug toxicity, environmental exposure (e.g. asbestos) or collagen vascular disease (e.g. scleroderma, rheumatoid arthritis).

Epidemiology

It tends to be commoner in males with most cases presenting in those over 50 years of age.

Diagnostic criteria

ATS-ERS (American Thoracic Society and European Respiratory Society) major and minor criteria for the diagnosis of IPF in the absence of a surgical lung biopsy 5.

Major criteria
  • exclusion of other known causes of interstitial lung disease (e.g. toxic effects of certain drugs, environmental exposures, connective tissue diseases) abnormal results of pulmonary function studies, including evidence of restriction (reduced vital capacity, often with an increased FEV1/FVC ratio) and impaired gas exchange (increased PaO2, decreased PaO2 with rest or exercise, or decreased DlCO)
  • bibasilar reticular abnormalities with minimal ground-glass opacities at high-resolution CT
  • transbronchial lung biopsy or bronchoalveolar lavage shows no features to support an alternative diagnosis
Minor criteria
  • age > 50 years
  • insidious onset of otherwise unexplained dyspnea on exertion
  • duration of illness being over 3 months
  • bibasilar inspiratory crackles (dry or “Velcro” type)

Pathology

Histology

UIP pattern is characterized by spatial and temporal heterogeneity. Spatial heterogeneity denote biopsy sample showing patchy lung involvement with normal lung interspace between diseased lung. Temporal heterogeneity denotes different stages of disease seen on a single specimen, including normal lung, interstitial inflammation, interstitial fibrosis and fibroblastic foci 4.

Radiographic features

The CT imaging findings complements the histology. It is more correct to describe characteristic imaging pattern as UIP rather than IPF,  a terminology assigned for the idiopathic clinical syndrome of UIP.

UIP-pattern of fibrosis is characterised by honeycombing cysts and reticular septal thickening with subpleural and posterior basal predominance. Traction bronchiectasis can also be observed, however, this is a general feature of fibrosis not specific to UIP-pattern 4.In a subgroup of patients the imaging finding of UIP overlap with NSIP and biopsy may be necessary to obtained the correct diagnosis.

Treatment and prognosis

The clinical course is that of gradual deterioration and the condition carries a rather poor prognosis with median survival ranging from 2.5 to 3.5 years from the time of diagnosis (at the time of initial writing) 2. Some reportes have suggested a slowing of progression with treatment by Pirfenidone 7-8.

Differential diagnosis

Consider pulmonary fibrosis due to a known cause, such as

See also

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